Apparatus and method for selecting best beam in wireless communication system

ABSTRACT

An apparatus and method for selecting the best beam in a wireless communication system are provided. An operation of a Base Station (BS) includes repeatedly transmitting reference signals beamformed with a first width, receiving a feedback signal indicating at least one preferred-beam having the first width from at least one terminal, determining a direction range within which reference signals beamformed with a second width are to be transmitted and a transmission pattern, based on the at least one preferred-beam having the first width, repeatedly transmitting the reference signals beamformed with the second width within the determined direction range according to the transmission pattern, and receiving a feedback signal indicating at least one preferred-beam having the second width from the at least one terminal.

PRIORITY

This application claims the benefit under 35 U.S.C. §119(a) of a KoreanPatent Application on Sep. 1, 2011 filed in the Korean IntellectualProperty Office and assigned Serial No. 10-2011-0088441, the entiredisclosure of which are herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication system. Moreparticularly, the present invention relates to an apparatus and methodfor selecting the best beam in a wireless communication system which isperforming beam forming

2. Description of the Related Art

To meet the ever-increasing demand for wireless data traffic, a wirelesscommunication system is being developed to support a higher datatransmission rate. To increase a data transmission rate, a4th-Generation (4G) system that is now being commercialization pursuedtechnology development mainly to improve spectral efficiency. However,it has become difficult to meet the explosively increasing demand ofwireless data traffic with only the spectral efficiency improvementtechnology.

A way for solving the above problem is using a very wide frequency band.A frequency band presently used in a mobile communication cellularsystem is generally 10 Giga Hertz (GHz) or less, and there is a greatdifficulty in securing a wide frequency band. Accordingly, there is aneed to secure a broadband frequency at a higher frequency band.However, as a frequency for wireless communication increases, apropagation path loss increases. Due to this, a wave reach distancebecomes relatively short, thereby causing a decrease of servicecoverage. One technology for solving this (i.e., for decreasing thepropagation path loss to increase the wave reach distance) is abeamforming technology.

The beamforming can be divided into transmit beamforming and receivebeamforming. The transmit beamforming generally concentrates wave reachcoverage on a specific direction using a plurality of antennas.Generally, a form of gathering the plurality of antennas is called anantenna array, and an individual antenna included in the antenna arrayis called an array element. If the transmit beamforming is applied, asignal transmission distance increases and simultaneously, a signal isconcentrated in an intended direction (e.g., a signal is almost nottransmitted in directions other than an intended direction).Accordingly, there is an advantage in which interference in other usersgreatly decreases. The receive beamforming concentrates wave receptionon a specific direction using a reception antenna array at receptionside. Consequently, the sensitivity of a signal received in an intendeddirection is increased and, by excluding a signal coming in directionsother than the intended direction, an interfering signal is cut off.

As described above, the introduction of a very high frequency (i.e.,millimeter (mm)) wave system is expected to secure a wide frequencyband. In this case, to overcome a propagation path loss, a beamformingtechnology is being taken into consideration. Accordingly, there shouldbe proposed an alternative for effectively performing beamforming undera mobile communication environment in which users travel and apropagation environment changes.

Therefore, a need exists for an apparatus and method for performingeffective beamforming in a wireless communication system. In addition, aneed exists for an alternative for decreasing a system overhead andsimultaneously obtaining a sufficient antenna gain suitably usingvarious beam patterns.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present invention.

SUMMARY OF THE INVENTION

Aspects of the present invention are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages below. Accordingly, an aspect of the present invention isto provide an apparatus and method for performing effective beamformingin a wireless communication system.

Another aspect of the present invention is to provide an apparatus andmethod for selecting the best beam in a wireless communication system.

A further aspect of the present invention is to provide an apparatus andmethod for minimizing a signaling overhead for selection of the bestbeam in a wireless communication system.

The above aspects are achieved by providing an apparatus and method forselecting the best beam in a wireless communication system.

According to an aspect of the present invention, an operation method ofa Base Station (BS) in a wireless communication system is provided. Themethod includes repeatedly transmitting reference signals beamformedwith a first width, receiving a feedback signal indicating at least onepreferred-beam having the first width from at least one terminal,determining a direction range within which reference signals beamformedwith a second width are to be transmitted and a transmission pattern,based on the at least one preferred-beam having the first width,repeatedly transmitting the reference signals beamformed with the secondwidth within the determined direction range according to thetransmission pattern, and receiving a feedback signal indicating atleast one preferred-beam having the second width from the at least oneterminal. The first width is greater than the second width.

According to another aspect of the present invention, an operationmethod of a terminal in a wireless communication system is provided. Themethod includes measuring a reception signal strength for referencesignals beamformed with a first width which are received from a BS,transmitting a feedback signal indicating a preferred-beam having thefirst width, to the BS, determining transmission patterns of referencesignals beamformed with a second width corresponding to the direction ofthe preferred-beam having the first width of the at least one terminalhaving accessed the BS, measuring a reception signal strength for thereference signals beamformed with the second width which are receivedaccording to the determined transmission patterns, and transmitting afeedback signal indicating a preferred-beam having the second width, tothe BS. The first width is greater than the second width.

According to a further another aspect of the present invention, a BSapparatus in a wireless communication system is provided. The apparatusincludes a beamforming unit, a receiver, and a controller. Thebeamforming unit beamforms reference signals with a beam having a firstwidth and a beam having a second width. The receiver receives a feedbacksignal indicating at least one preferred-beam having a first width and afeedback signal indicating at least one preferred-beam having a secondwidth from at least one terminal. The controller controls to repeatedlytransmit the reference signals beamformed with the first width, ifreceiving the feedback signal indicating at least one preferred-beamhaving the first width from the at least one terminal, determine adirection range within which reference signals beamformed with a secondwidth are to be transmitted and a transmission pattern depending on theat least one preferred-beam having the first width, and to repeatedlytransmit the reference signals beamformed with the second width withinthe determined direction range according to the transmission pattern.The first width is greater than the second width.

According to a yet another aspect of the present invention, a terminalapparatus in a wireless communication system is provided. The apparatusincludes a modem, a controller, and a transmitter. The modem measures areception signal strength for reference signals beamformed with a firstwidth which are received from a BS, and measures a reception signalstrength for reference signals beamformed with a second width which arereceived from the BS according to transmission patterns of the referencesignals beamformed with the second width. The controller controls todetermine a preferred-beam having the first width based on the receptionsignal strength for the reference signals beamformed with the firstwidth, determine the transmission patterns of the reference signalsbeamformed with the second width corresponding to the direction of thepreferred-beam having the first width of the at least one terminalhaving accessed the BS, and determine the preferred-beam having thesecond width based on the reception signal strength for the referencesignals beamformed with the second width. The transmitter transmits afeedback signal indicating the preferred-beam having the 1st width afeedback signal indicating the preferred-beam having the second width,to the BS. The first width is greater than the second width.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating an example of a beam pattern in awireless communication system according to an exemplary embodiment ofthe present invention;

FIG. 2 is a diagram schematically illustrating a beam acquisitionprocedure using only a narrow beam in a wireless communication systemaccording to an exemplary embodiment of the present invention;

FIGS. 3A and 3B are diagrams schematically illustrating a beamacquisition procedure using all of a wide beam and a narrow beam in awireless communication system according to an exemplary embodiment ofthe present invention;

FIG. 4 is a diagram illustrating signaling for beam acquisition in awireless communication system according to a first exemplary embodimentof the present invention;

FIG. 5 is a diagram illustrating signaling for beam acquisition in awireless communication system according to a second exemplary embodimentof the present invention;

FIG. 6 is a diagram illustrating signaling for beam acquisition in awireless communication system according to a third exemplary embodimentof the present invention;

FIG. 7 is a flowchart illustrating an operation procedure of a BaseStation (BS) for selection of the best beam in a wireless communicationsystem according to an exemplary embodiment of the present invention;

FIG. 8 is a flowchart illustrating an operation procedure of a terminalfor selection of the best beam in a wireless communication systemaccording to an exemplary embodiment of the present invention;

FIG. 9 is a block diagram illustrating a construction of a BS in awireless communication system according to an exemplary embodiment ofthe present invention; and

FIG. 10 is a block diagram illustrating a construction of a terminal ina wireless communication system according to an exemplary embodiment ofthe present invention.

Throughout the drawings, it should be noted that like reference numbersare used to depict the same or similar elements, features, andstructures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the embodiments described hereincan be made without departing from the scope and spirit of theinvention. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of theinvention. Accordingly, it should be apparent to those skilled in theart that the following description of exemplary embodiments of thepresent invention is provided for illustration purpose only and not forthe purpose of limiting the invention as defined by the appended claimsand their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

A technology for selecting the best beam in a wireless communicationsystem according to exemplary embodiments of the present invention isdescribed below. As an example, the following description is made for anOrthogonal Frequency Division Multiplexing/Orthogonal Frequency DivisionMultiple Access (OFDM/OFDMA) wireless communication system.

According to exemplary embodiments of the present invention, a cellularsystem operating at a very high frequency band decreases a highpropagation path loss by virtue of an antenna gain obtained through abeamforming technology. The beamforming technology is a technique fortransmitting signals from a plurality of antennas so that the signalscan be gathered to a specific direction. For this, a transmit endadjusts a phase of a signal transmitted from every each antenna, therebyconcentrating the signals transmitted from all of the antennas on thespecific direction and as a result, the transmit end is able to obtain ahigh antenna gain. A variable related to the antenna gain is the numberof antennas used for transmitting the signals. As the number of antennasincreases, an antenna gain can be increasingly obtained. As the numberof antennas increases, a beam pattern or beam width formed by themultiple antennas gets narrower. For example, signals transmitted fromthe plurality of antennas are more intensively gathered to a specificdirection, whereby a high antenna gain is obtained.

FIG. 1 illustrates an example of a beam pattern in a wirelesscommunication system according to an exemplary embodiment of the presentinvention.

Referring to FIG. 1, a Base Station (BS) 100 is illustrated astransmitting a signal to a terminal A 110 and a terminal B 120.According to exemplary embodiments of the present invention, BS 100transmits the signal to terminal A 110 using a fewer number of antennasrelative to the number of antennas that the BS 100 uses for transmittingthe signal to terminal B 120. If BS 100 transmits a signal using fewerantennas, a beam of a wide beam width is formed like a beam pattern 115formed toward a terminal A 110. In such an example, because the signalis forwarded in a wide direction, an antenna gain in a specificdirection is not high. In contrast, if the BS 100 transmits a signalusing many antennas, a beam of a narrow beam width is formed like a beampattern 125 formed toward a terminal B 120. In such an example, becausea signal is not propagated in directions other than a specificdirection, a high antenna gain is expected.

In a case of constructing antennas to provide a wide beam width like thebeam pattern 115, an antenna gain is low but it can support a widedirection, so there is an advantage of decreasing a system overheadnecessary for beam acquisition. In contrast, in a case of constructingantennas to provide a narrow beam width like the beam pattern 125, ahigh antenna gain is expected but a serviceable area is small because ofthe narrow beam width, so there is a disadvantage of increasing a systemoverhead necessary for beam acquisition. Accordingly, there is a needfor an alternative for decreasing a system overhead and simultaneouslyobtaining a sufficient antenna gain suitably using various beampatterns.

A cellular system using a very high frequency band suffers largepropagation path damage due to a frequency characteristic. Accordingly,the cellular system guarantees sufficient antenna gains for all of acontrol signal and a data signal. For this, a beam acquisition procedurefor determining the best beam between a BS and a terminal is performed.

FIG. 2 schematically illustrates a beam acquisition procedure using onlya narrow beam in a wireless communication system according to anexemplary embodiment of the present invention.

Referring to FIG. 2, a terminal A 210, a terminal B 220, and a terminalC 230 are located within one sector. A BS 200 beamforms referencesignals to narrow beams, and repeatedly transmits a plurality ofreference signals in all directions within the sector. For example, theBS 200 multiplexes and transmits a plurality of narrow beams headingtoward different directions within the sector in a time or frequencydivision scheme. For example, the BS 200 turns a beam direction in thedirection of an arrow illustrated in FIG. 2 while sequentiallytransmitting reference signals beamformed with narrow beams. Theterminals 210, 220, and 230 each receive reference signals repeatedlytransmitted through resources of a corresponding time duration orfrequency duration, and measure reception signal strengths for therespective reference signals. The terminals 210, 220, and 230 eachselect transmission beams having the maximum signal strengths, andnotify the BS 200 of the corresponding selected transmission beams.

In a case of the beam acquisition procedure illustrated in FIG. 2, dueto a narrow beam width, the number of reference signals or transmissionsthereof is relatively large, thereby causing a high system overhead.Accordingly, exemplary embodiments of the present invention furtherproposes a beam acquisition procedure capable of decreasing the numberof reference signals or the transmissions thereof and simultaneouslyobtaining a sufficient antenna gain.

FIGS. 3A and 3B schematically illustrate a beam acquisition procedureusing all of a wide beam and a narrow beam in a wireless communicationsystem according to an exemplary embodiment of the present invention.The beam acquisition procedure using all of the wide beam and the narrowbeam comprises two steps. FIG. 3A illustrates a 1st step of the beamacquisition procedure, and FIG. 3B illustrates a 2nd step of the beamacquisition procedure.

Referring to FIG. 3A, the 1st step of the beam acquisition procedureuses a beam having a wide beam width. For example, a BS 300 beamformsreference signals to wide beams, and repeatedly transmits the referencesignals having wide beam widths in all directions within a sectorthrough a resource of a constant time and frequency duration. In such anexample, because the wide beams are used, the number of symbolsnecessary for repeated transmission of reference signals is decreasedcompared to the example illustrated in FIG. 2. According to this,terminals 310, 320, and 330 each measure reception signal strengths forreference signals and select wide beams having maximum reception signalstrengths, as preferred-wide beams. At this time, the number ofpreferred-wide beams becomes different depending on a form of thedistribution of the terminals located within one sector. For example, ifall terminals are located intensively in the service coverage of onewide transmission beam, then only the one wide transmission beam isselected as a wide beam that the terminals all prefer. However, ifterminals are uniformly distributed within one sector, then the wholewide transmission beams are selected as wide beams that the terminalseach prefer. In FIG. 3A, the terminal A 310 and the terminal B 320prefer a 2nd wide beam, and the terminal C 330 prefers a 4th wide beam.For example, among the whole five wide beams, only the two wide beamsare selected as preferred-wide beams. According to this, the terminals310, 320, and 330 each notify the BS 300 of their own preferred-widebeams. That is, the terminals 310, 320, and 330 each feed backinformation indicating the preferred-wide beams, to the BS 300.

Referring to FIG. 3B, the 2nd step of the beam acquisition procedureuses a beam having a narrow beam width. For example, the BS 300beamforms reference signals to narrow beams, and repeatedly transmitsthe reference signals having narrow beam widths. At this time, the BS300 determines a direction range to which the reference signals havingthe narrow beam widths are to be transmitted, considering thepreferred-wide beam confirmed in the 1st step, and repeatedly transmitsthe reference signals having the narrow beam widths only within thedetermined range. For example, the BS 300 transmits the referencesignals having the narrow beam widths only within a propagation range ofat least one wide beam selected as a preferred-wide beam in the 1ststep. It cannot be said that all terminals are always uniformlydistributed within a sector. For example, the terminals can bedistributed intensively in a partial area. Therefore, there is no needto transmit the reference signals having the narrow beam widths in alldirections all the time. Through this, the BS 300 can excludeunnecessary transmission of reference signals. For example, when twowide beams that the terminals 310, 320, and 330 within the sector preferare determined as in FIG. 3A, the BS 300 minutely turns a beam directionwhile sequentially transmitting the reference signals having the narrowbeam widths to the terminals 310, 320, and 330 only within thepropagation coverage of the two preferred-wide beams. Therefore, theterminals 310, 320, and 330 each measure reception signal strengths forthe reference signals having the narrow beam widths, select narrow beamshaving maximum signal strengths as preferred-narrow beams, and notifythe BS 300 of the preferred-narrow beams. As an example, the terminals310, 320, and 330 each feed back information indicating thepreferred-narrow beams, to the BS 300.

Through the procedures of FIG. 3A and FIG. 3B, each terminal candetermine a preferred-narrow beam. For example, irrespective of thenumber of terminals, the number of preferred-wide beams is determined ina 1st step, and a preferred-narrow beam in the direction of thepreferred-wide beam is determined in a 2nd step. Accordingly, ifterminals are randomly distributed in the whole coverage within asector, reference signals having narrow beam widths are transmitted onlyin a specific direction, such that the number of transmission of thereference signals is decreased. Because the 1st step uses wide beams, aburden of a system overhead is not large. Accordingly, in a case where a2-step beam acquisition way of FIG. 3A and FIG. 3B is employed, asufficient antenna gain can be obtained even with only a small overhead,depending on a position of a terminal within a sector.

A detailed exemplary embodiment of the present invention for determiningthe best beam according to the aforementioned scheme is described below.For description convenience below, exemplary embodiments of the presentinvention refers to the ‘reference signal beamformed with wide beam’ asa ‘wide beam reference signal’, and refers to the ‘reference signalbeamformed with narrow beam’ as a ‘narrow beam reference signal’.

In an exemplary embodiment of the present invention described below, itis assumed that a terminal is aware of system configuration informationsuch as the number of wide beams used in a BS, the number of narrowbeams corresponding to each wide beam, a position of a resource throughwhich a wide beam is transmitted, a position of a resource through whicha narrow beam is transmitted, and the like. For example, the systemconfiguration information can be predefined and stored in the terminalat the time of terminal manufacturing, or can be provided to theterminal periodically during an initial entry process of the BS orthrough a Broadcast Channel (BCH). Also, in an exemplary embodiment ofthe present invention described below, even other information predefinedbetween the BS and the terminal can be provided to the terminal as thesystem configuration information. Furthermore, in a case in which a BSaccording to an exemplary embodiment of the present invention cansupport all of exemplary embodiments described below and selectivelycarry out only one of the exemplary embodiments below, the BS canprovide the terminal with indication information of notifying whichexemplary embodiment the BS performs, as the system configurationinformation.

FIG. 4 illustrates signaling for beam acquisition in a wirelesscommunication system according to an exemplary embodiment of the presentinvention.

Referring to FIG. 4, in step 401, a BS 400 repeatedly transmits widebeam reference signals beamformed with wide beams, in all directionswithin a sector. The wide beam reference signals can be transmitted in aform of a synchronization channel, a preamble, a midamble and the like.As an example, exemplary embodiments of the present invention assumethat all directions within one sector are supported by four wide beams.According to this, the BS 400 sequentially transmits four wide beamreference signals.

As the wide beam reference signals are transmitted in all the directionswithin the sector, in step 403, a terminal 410 determines apreferred-wide beam, and feeds back information indicating thepreferred-wide beam, to the BS 400. In other words, the terminal 410measures a reception signal strength for each of the wide beam referencesignals and determines, as the preferred-wide beam, a wide beamcorresponding to a reference signal having a maximum reception signalstrength. As an example, the terminal 410 determines which of the widebeam reference signals transmitted by the BS 400 corresponds to thepreferred-wide beam. According to exemplary embodiments of the presentinvention, the terminal 410 can determine two or more wide beams aspreferred-wide beams. For example, exemplary embodiments of the presentinvention assume that two wide beams are determined as thepreferred-wide beams.

After that, in step 405, the BS 400 receives information indicatingpreferred-wide beams from all terminals within a sector including theterminal 410 and then, transmits beam pattern information notifyingtransmission patterns of narrow beam reference signals to be transmittedhereafter, to the terminals. The beam pattern information can beconstructed in an indexing scheme, a bitmap scheme, and the like. In acase of a 2-step beam acquisition procedure according to an exemplaryembodiment of the present invention, measurement durations during whichnarrow beam reference signals are transmitted are continuousirrespective of the results of selection of preferred-wide beams.Accordingly, a position of a frame during which narrow beam referencesignals corresponding to each preferred-wide beam are transmittedbecomes different depending on the number of preferred-wide beams.However, the number and direction of the whole preferred-wide beams areknown to only the BS 400, such that the terminal 410 cannot be aware ofthe number and direction of preferred-wide beams other than its ownpreferred-wide beam and accordingly, cannot be aware of the transmissionpatterns of the narrow beam reference signals. Therefore, the BS 400provides information notifying the transmission patterns of the narrowbeam reference signals to be transmitted hereafter, to the terminals.

For example, if the terminal 410 can know whether narrow beam referencesignals corresponding to a preferred-narrow beam are transmitted throughany frames, in other words, if the terminal 410 can know a correspondingrelationship between a preferred-wide beam and a frame, then theterminal 410 can detect the narrow beam reference signal only in framescorresponding to its own preferred-wide beam. Accordingly, the beampattern information can include information notifying the correspondingrelationship between the preferred-wide beam and the frame. Here, when anarrow beam reference signal is transmitted according to the order of anindex of a wide beam, the corresponding relationship between thepreferred-wide beam and the frame can be expressed by an index of atleast one preferred-wide beam confirmed in the BS 400. Or, thecorresponding relationship between the preferred-wide beam and the framecan be expressed by a combination of an index of each preferred-widebeam and an index of a corresponding frame.

As another example, if the terminal 410 can know the number of narrowbeam reference signals to be transmitted hereafter, the terminal 410 candetect all the narrow beam reference signals. Accordingly, the beampattern information can include information notifying the number ofnarrow beam reference signals to be transmitted. Here, the number ofnarrow beam reference signals to be transmitted can be indirectexpressed through the number of frames in which the narrow beamreference signals are to be transmitted, the number of preferred-widebeams, an index of the last one of frames in which the narrow beamreference signals are to be transmitted and the like.

For example, the beam pattern information can include at least one of anindex of a preferred-wide beam, a combination of an index of apreferred-wide beam and an index of a corresponding frame, the number ofnarrow beam reference signals to be transmitted, the number of frames inwhich the narrow beam reference signals are to be transmitted, thenumber of preferred-wide beams, and an index of the last one of framesin which the narrow beam reference signals are to be transmitted.

Next, in step 407 to step 413, the BS 400 determines a direction rangeover which it is to transmit narrow beam reference signals depending onat least one preferred-wide beam and then, repeatedly transmits thenarrow beam reference signals within the determined range. The narrowbeam reference signal can be transmitted in a form of a pilot symbol. Indetail, the BS 400 determines a propagation range of the at least onepreferred-wide beam as the direction range over which it is to transmitthe narrow beam reference signals. And, the BS 400 minutely turns a beamdirection within the determined range while sequentially transmittingthe narrow beam reference signals. Here, exemplary embodiments of thepresent invention assume that one wide beam reference signal correspondsto four narrow beam reference signals, and that two narrow beamreference signals per frame are transmitted. In this case, asillustrated in FIG. 4, when two preferred-wide beams are selected, theBS 400 transmits the total eight narrow beam reference signals throughfour frames (e.g., as illustrated at steps 407, 409, 411, and 413).According to another exemplary embodiment of the present invention, theframe of FIG. 4 can be substituted with a super frame. The super framemeans a bundle of multiple frames.

As the narrow beam reference signals are transmitted within thepropagation ranges of the preferred-wide beams, in step 415, theterminal 410 determines a preferred-narrow beam, and feeds backinformation indicating the preferred-narrow beam, to the BS 400. Inother words, the terminal 410 measures a reception signal strength foreach of the narrow beam reference signals and determines, as thepreferred-narrow beam, a narrow beam corresponding to a reference signalhaving a maximum reception signal strength. At this time, the terminal410 can grasp transmission patterns of the narrow beam reference signalsthrough the beam pattern information, and detect the narrow beamreference signals according to the transmission patterns. Particularly,when the beam pattern information transmitted in step 405 includesinformation notifying a corresponding relationship between apreferred-wide beam and a frame, the terminal 410 can detect the narrowbeam reference signals only in frames corresponding to its ownpreferred-wide beam.

In FIG. 4, the terminal 410 receives the last narrow beam referencesignal in an (n+3)th frame, and feeds back information indicating apreferred-narrow beam to the BS 400 in the (n+3)th frame. But, a timepoint of feedback of the information indicating the preferred-narrowbeam illustrated in FIG. 4 is one example and, according to anotherexemplary embodiment of the present invention, the terminal 410 can feedback the information indicating the preferred-narrow beam after the(n+3)th frame.

FIG. 5 illustrates signaling for beam acquisition in a wirelesscommunication system according to a second exemplary embodiment of thepresent invention.

Referring to FIG. 5, in step 501, a BS 500 repeatedly transmits widebeam reference signals beamformed with wide beams, in all directionswithin a sector. The wide beam reference signals can be transmitted in aform of a synchronization channel, a preamble, a midamble, and the like.Here, the exemplary embodiment of the present invention assumes that alldirections within one sector are supported by four wide beams. Accordingto this, the BS 500 sequentially transmits four wide beam referencesignals.

As the wide beam reference signals are transmitted in all the directionswithin the sector, in step 503, a terminal 510 determines apreferred-wide beam, and feeds back information indicating thepreferred-wide beam, to the BS 500. In other words, the terminal 510measures a reception signal strength for each of the wide beam referencesignals and determines, as the preferred-wide beam, a wide beamcorresponding to a reference signal having a maximum reception signalstrength. As an example, the terminal 510 determines which of the widebeam reference signals transmitted by the BS 500 corresponds to thepreferred-wide beam. According to exemplary embodiments of the presentinvention, the terminal 510 can determine two or more wide beams aspreferred-wide beams. An exemplary embodiment of the present inventionassumes that two wide beams are determined as the preferred-wide beams.

After that, in step 505, the BS 500 receives information indicatingpreferred-wide beams from all terminals within a sector including theterminal 510 and then, transmits beam pattern information notifyingtransmission patterns of narrow beam reference signals to be transmittedhereafter, to the terminals. The beam pattern information can beconstructed in an indexing scheme, a bitmap scheme, and the like. In acase of a 2-step beam acquisition procedure according to an exemplaryembodiment of the present invention, measurement durations during whichnarrow beam reference signals are transmitted are continuousirrespective of the results of selection of preferred-wide beams.Accordingly, a position of a frame during which narrow beam referencesignals corresponding to each preferred-wide beam are transmittedbecomes different depending on the number of preferred-wide beams.However, the number and direction of the whole preferred-wide beams areknown to only the BS 500, such that the terminal 510 cannot be aware ofthe number and direction of preferred-wide beams other than its ownpreferred-wide beam and accordingly, cannot be aware of the transmissionpatterns of the narrow beam reference signals. Therefore, the BS 500provides information notifying the transmission patterns of the narrowbeam reference signals to be transmitted hereafter, to the terminals.

For example, if the terminal 510 can know whether narrow beam referencesignals corresponding to a preferred-narrow beam are transmitted throughany frame, in other words, if the terminal 510 can know a correspondingrelationship between a preferred-wide beam and a frame, the terminal 510can detect the narrow beam reference signals only in a framecorresponding to its own preferred-wide beam. Accordingly, the beampattern information can include information notifying the correspondingrelationship between the preferred-wide beam and the frame. Here, when anarrow beam reference signal is transmitted according to the order of anindex of a wide beam, the corresponding relationship between thepreferred-wide beam and the frame can be expressed by an index of atleast one preferred-wide beam confirmed in the BS 500. Or, thecorresponding relationship between the preferred-wide beam and the framecan be expressed by a combination of an index of each preferred-widebeam and an index of a corresponding frame.

As another example, if the terminal 510 can know the number of narrowbeam reference signals to be transmitted hereafter, the terminal 510 candetect all the narrow beam reference signals. Accordingly, the beampattern information can include information notifying the number ofnarrow beam reference signals to be transmitted. Here, the number ofnarrow beam reference signals to be transmitted can be indirectexpressed through the number of frames in which the narrow beamreference signals are to be transmitted, the number of preferred-widebeams, an index of the last one of frames in which the narrow beamreference signals are to be transmitted and the like.

For example, the beam pattern information can include at least one of anindex of a preferred-wide beam, a combination of an index of apreferred-wide beam and an index of a corresponding frame, the number ofnarrow beam reference signals to be transmitted, the number of frames inwhich the narrow beam reference signals are to be transmitted, thenumber of preferred-wide beams, and an index of the last one of framesin which the narrow beam reference signals are to be transmitted.

Next, in step 507 and step 509, the BS 500 determines a direction rangeover which it is to transmit narrow beam reference signals depending onat least one preferred-wide beam and then, repeatedly transmits thenarrow beam reference signals within the determined range. The narrowbeam reference signal can be transmitted in a form of a pilot symbol. Indetail, the BS 500 determines a propagation range of the at least onepreferred-wide beam as the direction range over which it is to transmitthe narrow beam reference signals. And, the BS 500 minutely turns a beamdirection within the determined range while sequentially transmittingthe narrow beam reference signals. Here, exemplary embodiments of thepresent invention assume that one wide beam reference signal correspondsto four narrow beam reference signals, and four narrow beam referencesignals per frame are transmitted. In this case, as illustrated in FIG.5, when two preferred-wide beams are selected, the BS 500 transmits thetotal eight narrow beam reference signals through two frames (e.g., asillustrated at steps 507 and 509). According to another exemplaryembodiment of the present invention, the frame of FIG. 5 can besubstituted with a super frame. The super frame means a bundle ofmultiple frames.

As the narrow beam reference signals are transmitted within thepropagation ranges of the preferred-wide beams, in step 511, theterminal 510 determines a preferred-narrow beam, and feeds backinformation indicating the preferred-narrow beam, to the BS 500. Inother words, the terminal 510 measures a reception signal strength foreach of the narrow beam reference signals and determines, as thepreferred-narrow beam, a narrow beam corresponding to a reference signalhaving a maximum reception signal strength. At this time, the terminal510 can grasp transmission patterns of the narrow beam reference signalsthrough the beam pattern information, and detect the narrow beamreference signals according to the transmission patterns. Particularly,when the beam pattern information transmitted in step 505 includesinformation notifying a corresponding relationship between apreferred-wide beam and a frame, the terminal 510 can detect the narrowbeam reference signals only in a frame corresponding to its ownpreferred-wide beam.

In FIG. 5, the terminal 510 receives the last narrow beam referencesignal in an (n+1)th frame, and feeds back information indicating apreferred-narrow beam to the BS 500 in the (n+1)th frame. But, a timepoint of feedback of the information indicating the preferred-narrowbeam illustrated in FIG. 5 is one example and, according to anotherexemplary embodiment of the present invention, the terminal 510 can feedback the information indicating the preferred-narrow beam after the(n+1)th frame.

The comparison of the exemplary embodiment of the present inventionillustrated in FIG. 4 and the exemplary embodiment of the presentinvention illustrated in FIG. 5 is given as follows. The exemplaryembodiment of the present invention illustrated in FIG. 4 transmits twonarrow beam reference signals per frame, and the exemplary embodiment ofthe present invention illustrated in FIG. 5 transmits four narrow beamreference signals per frame. According to this, in the exemplaryembodiment of the present invention illustrated in FIG. 4, an overheadcaused by reference signals per frame is relatively less. However, inthe exemplary embodiment of the present invention illustrated in FIG. 4,a time required for completing transmission of narrow beam referencesignals is relatively long. Accordingly, the exemplary embodiment of thepresent invention illustrated in FIG. 4 is advantageous to a service notsensitive to a time delay, and the exemplary embodiment of the presentinvention illustrated in FIG. 5 is advantageous to a serviceguaranteeing a short time delay.

FIG. 6 illustrates signaling for beam acquisition in a wirelesscommunication system according to a third exemplary embodiment of thepresent invention.

Referring to FIG. 6, in step 601, a BS 600 repeatedly transmits widebeam reference signals beamformed with wide beams, in all directionswithin a sector. The wide beam reference signals can be transmitted in aform of a synchronization channel, a preamble, a midamble, and the like.Here, the exemplary embodiment of the present invention assumes that alldirections within one sector are supported by four wide beams. Accordingto this, the BS 600 sequentially transmits four wide beam referencesignals.

As the wide beam reference signals are transmitted in all the directionswithin the sector, in step 603, a terminal 610 determines apreferred-wide beam, and feeds back information indicating thepreferred-wide beam, to the BS 600. In other words, the terminal 610measures a reception signal strength for each of the wide beam referencesignals and determines, as the preferred-wide beam, a wide beamcorresponding to a reference signal having a maximum reception signalstrength. As an example, the terminal 610 determines which of the widebeam reference signals transmitted by the BS 600 corresponds to thepreferred-wide beam. According to exemplary embodiments of the presentinvention, the terminal 610 can determine two or more wide beams aspreferred-wide beams. An exemplary embodiment of the present inventionassumes that two wide beams are determined as the preferred-wide beams.

In the exemplary embodiment of the present invention illustrated in FIG.6, narrow beam reference signals are transmitted in a frame or superframe of a predefined position depending on a corresponding wide beamreference signal. For example, in a case in which narrow beam referencesignals are transmitted during four frames after completion of feedbackof preferred-wide beams, narrow beam reference signals to be transmittedin the direction of a 1st wide beam are transmitted during a 1st frame,narrow beam reference signals to be transmitted in the direction of a2nd wide beam are transmitted during a 2nd frame, narrow beam referencesignals to be transmitted in the direction of a 3rd wide beam aretransmitted during a 3rd frame, and narrow beam reference signals to betransmitted in the direction of a 4th wide beam are transmitted during a4th frame. Accordingly, when partial wide beams are not selected aspreferred-wide beams, partial frames corresponding to the non-selectedwide beams do not carry narrow beam reference signals. Accordingly,although terminals are not aware of the number of narrow beam referencesignals transmitted hereafter, the terminals can determine that thenarrow beam reference signals are transmitted in the direction of theirown preferred-wide beams during frames corresponding to their ownpreferred-wide beams. Therefore, in contrast to the exemplaryembodiments of the present invention illustrated in FIG. 4 and FIG. 5,in the exemplary embodiment illustrated in FIG. 6, the BS 600 does nottransmit beam pattern information. In this case, information about aposition of a frame during which narrow beams corresponding to each widebeam are transmitted can be periodically transmitted as systemconfiguration information during an initial entry process of theterminal 610 or through a BCH. However, according to another exemplaryembodiment of the present invention, the BS 600 can transmit beampattern information, which represents a corresponding relationshipbetween a wide beam and a frame, to a terminal to guarantee thecertainty of a narrow beam reception operation of the terminal.

Next, in step 605 and step 607, the BS 600 determines a direction rangethat is to transmit narrow beam reference signals and a frame dependingon at least one preferred-wide beam and then, repeatedly transmits thenarrow beam reference signals within the determined range through thedetermined at least one frame. The narrow beam reference signal can betransmitted in a form of a pilot symbol. In detail, the BS 600determines a propagation range of the at least one preferred-wide beamas the direction range that is to transmit the narrow beam referencesignals. And, the BS 600 minutely turns a beam direction within thedetermined range while sequentially transmitting the narrow beam widthreference signals through the determined at least one frame. Here, anexemplary embodiment of the present invention assumes that one wide beamreference signal corresponds to four narrow beam reference signals, andfour narrow beam reference signals per frame are transmitted. In thiscase, as illustrated in FIG. 6, when a 2nd wide beam and a 4th wide beamare selected as preferred-wide beams, the BS 600 transmits four narrowbeam reference signals within a propagation range of the 2nd wide beamthrough an (n+1)th frame, and four narrow beam reference signals withina propagation range of the 4th wide beam through an (n+3)th frame.According to another exemplary embodiment of the present invention, theframe of FIG. 6 can be substituted with a super frame. The super framemeans a bundle of multiple frames.

As the narrow beam reference signals are transmitted within thepropagation ranges of the preferred-wide beams, in step 609, theterminal 610 determines a preferred-narrow beam, and feeds backinformation indicating the preferred-narrow beam to the BS 600. In otherwords, the terminal 610 measures a reception signal strength for each ofthe narrow beam reference signals transmitted through the framecorresponding to its own preferred-wide beam and determines, as its ownpreferred-narrow beam, a narrow beam corresponding to a reference signalhaving a maximum reception signal strength.

In FIG. 6, the terminal 610 receives the last narrow beam referencesignal in the (n+3)th frame, and feeds back information indicating thepreferred-narrow beam to the BS 600 in the (n+3)th frame. But, a timepoint of feedback of the information indicating the preferred-narrowbeam illustrated in FIG. 6 is one example and, according to anotherexemplary embodiment of the present invention, the terminal 610 can feedback the information indicating the preferred-narrow beam after the(n+3)th frame.

In the exemplary embodiments of the present invention described withreference to FIG. 4 to FIG. 6, a BS minimizes transmission ranges ofnarrow beam reference signals using a wide beam reference signal.However, when terminals are uniformly distributed within a cell orsector, the BS transmits narrow beam reference signals in all directionsdespite transmission of the wide beam reference signal. In this case,the process of transmitting the wide beam reference signal is notgreatly meaningful. For example, when the terminals are uniformlydistributed within the cell or sector, the wide beam reference signalundesirably rather increases a system overhead and a time delay.

Accordingly, according to another exemplary embodiment of the presentinvention, before the execution of a beam acquisition procedure, a BScan determine transmission or non-transmission of wide beam referencesignal considering the distribution of terminals within a cell orsector. If it is determined that the terminals are uniformly distributedwithin the cell or sector, the BS omits the transmission of the widebeam reference signal, and transmits narrow beam reference signals inall directions within the cell or sector. In contrast, if it isdetermined that the terminals are randomly distributed within the cellor sector, as illustrated in FIG. 4 to FIG. 6, the BS determines adirection range that is to transmit narrow beam reference signals usinga wide beam reference signal and then, transmits the narrow beamreference signals.

For example, as a way of checking the distribution of terminals, alocation based system can be considered. The location based system canmeasure a location of a terminal using Global Positioning System (GPS)signals or transmission signals of neighboring BSs. Or, as a way ofchecking the distribution of terminals, a BS can use a beam acquisitionprocedure according to an exemplary embodiment of the present inventionwithout an additional procedure of checking the distribution of theterminals. That is, the beam acquisition procedure according to theexemplary embodiment of the present invention can be repeatedly executedperiodically or randomly in a system operation process. Accordingly, theBS can determine if the distribution of the terminals is uniform usingthe measurement result of a previously executed beam acquisitionprocedure.

Operations and constructions of a BS and a terminal performing a beamacquisition procedure as above are described below in detail withreference to the accompanying drawings.

FIG. 7 illustrates an operation procedure of a BS for selection of thebest beam in a wireless communication system according to an exemplaryembodiment of the present invention.

Referring to FIG. 7, in step 701, the BS determines if terminals areuniformly distributed within its service coverage. Here, the servicecoverage means a cell or sector. For example, whether the terminals areuniformly distributed within the service coverage can be determinedbased on location information of each terminal measured using GPSsignals or signals of neighboring BSs. As another example, whether theterminals are uniformly distributed within the service coverage can bedetermined based on measurement information of a previously executedbeam acquisition procedure according to an exemplary embodiment of thepresent invention.

If it is determined in step 701 that the terminals are uniformlydistributed within the service coverage, the BS proceeds to step 703 andrepeatedly transmits narrow beam reference signals in all directionswithin the service coverage. For example, the BS sequentially transmitsreference signals beamformed with narrow beams of different directions,without performing the step of transmitting wide beam reference signals.

In contrast, if it is determined in step 701 that the terminals arerandomly distributed within the service coverage, in other words, whenthe terminals are concentrated on a specific coverage or do not exist inthe specific coverage, the BS proceeds to step 705 and repeatedlytransmits wide beam reference signals in all directions within theservice coverage. For example, the BS sequentially transmits referencesignals beamformed with wide beams of different directions. Here, thewide beam reference signal can be transmitted in a form of asynchronization channel, a preamble, a midamble, and the like.

After transmitting the wide beam reference signals, the BS proceeds tostep 707 and confirms a preferred-wide beam of at least one terminalthrough a feedback signal received from the at least one terminalAccording to exemplary embodiments of the present invention, thefeedback signal includes information indicating the preferred-wide beamof the terminal having transmitted the feedback signal. The informationindicating the preferred-wide beam of the terminal can include an indexof a reference signal or an index of a beam.

After confirming the preferred-wide beam of the at least one terminal,the BS proceeds to step 709 and determines transmission patterns ofnarrow beam reference signals to be transmitted hereafter. Thetransmission pattern is an issue on whether to transmit any narrow beamreference signals, or whether to transmit narrow beam reference signalscorresponding to any wide beam through any measurement duration. Here,the measurement duration is indicated by a frame or super frame. Inother words, the BS determines whether to transmit any narrow beamreference signals depending on the preferred-wide beam of the at leastone terminal, or whether to transmit narrow beam reference signalscorresponding to any wide beam through any measurement duration. Forexample, as illustrated in FIG. 4 and FIG. 5, in a case in whichmeasurement durations during which narrow beam reference signals aretransmitted are continuous irrespective of the results of selection ofpreferred-wide beams, the BS determines the number of measurementdurations that are to transmit the narrow beam reference signals,depending on the number of preferred-wide beams of at least oneterminal. And, the BS allocates the continuous measurement durations tothe preferred-wide beams, and determines to transmit the narrow beamreference signals through the measurement duration allocated to thecorresponding preferred-wide beam. As another example, as illustrated inFIG. 6, in a case in which the distribution of measurement durationsduring which narrow beam reference signals are transmitted becomesdifferent depending on the results of selection of preferred-wide beams,the BS confirms a position of at least one measurement durationcorresponding to a preferred-wide beam of at least one terminalaccording to a predefined corresponding relationship therebetween, anddetermines to transmit the narrow beam reference signals through themeasurement duration corresponding to the corresponding preferred-widebeam.

After determining the transmission patterns of the narrow beam referencesignals, the BS proceeds to step 711 and transmits beam patterninformation notifying the transmission patterns of the narrow beamreference signals. For example, the beam pattern information can includeat least one of an index of a preferred-wide beam, a combination of anindex of a preferred-wide beam and an index of a correspondingmeasurement duration, the number of narrow beam reference signals to betransmitted, the number of measurement durations during which narrowbeam reference signals are to be transmitted, the number ofpreferred-wide beams, and an index of the last one of measurementdurations during which narrow beam reference signals are to betransmitted. However, when a corresponding relationship between apreferred-wide beam and a measurement duration is predefined, step 711can be omitted. For example, in a case of the exemplary embodiment ofthe present invention illustrated in FIG. 6, step 711 can be omitted.

Next, the BS proceeds to step 713 and repeatedly transmits narrow beamreference signals within a propagation range of the preferred-wide beam.At this time, the BS transmits the narrow beam reference signalsaccording to the transmission patterns. For example, as illustrated inFIG. 4 and FIG. 5, the BS transmits narrow beam reference signalsthrough continuous measurement durations. For another example, asillustrated in FIG. 6, the BS transmits narrow beam reference signalsthrough measurement durations of a position corresponding to thepreferred-wide beam.

After repeatedly transmitting the narrow beam reference signals in step703 or step 713, the BS proceeds to step 715 and confirms apreferred-narrow beam of at least one terminal through a feedback signalreceived from the at least one terminal. The feedback signal includesinformation indicating the preferred-narrow beam of the at least oneterminal having transmitted the feedback signal. The informationindicating the preferred-narrow beam can include an index of a referencesignal or an index of a beam.

The method described above in relation with FIG. 7 under of the presentinvention may be provided as one or more instructions in one or moresoftware modules, or computer programs stored in an electronic deviceincluding the BS.

FIG. 8 illustrates an operation procedure of a terminal for selection ofthe best beam in a wireless communication system according to anexemplary embodiment of the present invention.

Referring to FIG. 8, in step 801, the terminal measures a receptionsignal strength for wide beam reference signals received from a BS. Thewide beam reference signals are repeatedly transmitted in all directionswithin the service coverage of the BS. The wide beam reference signalscan be transmitted in a form of a synchronization channel, a preamble,and a midamble and the like.

After measuring the reception signal strength for the wide beamreference signals, the terminal proceeds to step 803 and transmits afeedback signal notifying a preferred-wide beam of the terminal, to theBS. The feedback signal includes information indicating thepreferred-wide beam of the terminal. The information indicating thepreferred-wide beam of the terminal can include an index of a referencesignal or an index of a beam. At this time, the terminal can determinetwo or more wide beams as preferred-wide beams.

Next, the terminal proceeds to step 805 and confirms transmissionpatterns of narrow beam reference signals to be received hereafter.According to an exemplary embodiment of the present invention, theterminal can determine the transmission patterns depending on beampattern information provided from the BS. For example, the beam patterninformation can include at least one of an index of a preferred-widebeam, a combination of an index of a preferred-wide beam and an index ofa corresponding measurement duration, the number of reference signalsbeamformed with a 2nd width to be transmitted, the number of measurementdurations during which reference signals beamformed with a 2nd width areto be transmitted, the number of preferred-wide beams, and an index ofthe last one of measurement durations during which reference signalsbeamformed with a 2nd width are to be transmitted. In detail, theterminal receives the beam pattern information notifying thetransmission patterns from the BS, and determines the number of narrowbeam reference signals to be received, through the beam patterninformation. And, the terminal confirms a measurement duration allocatedto its preferred-wide beam through the beam pattern information. Here,the measurement duration allocated to the preferred-wide beam isdetermined according to the order of an index of the preferred-wide beamthat the terminal prefers among the whole preferred-wide beams.

According to another exemplary embodiment of the present invention, theterminal confirms a measurement duration corresponding to apreferred-wide beam according to a predefined corresponding relationshiptherebetween. In detail, the terminal is aware of the predefinedcorresponding relationship between the preferred-wide beam and themeasurement duration irrespective of the number and direction ofpreferred-wide beams and, according to this, the terminal can determinea corresponding measurement duration according to the order of an indexof a preferred-wide beam that the terminal prefers.

After confirming the transmission patterns of the narrow beam referencesignals, the terminal proceeds to step 807 and measures a receptionsignal strength for narrow beam reference signals received from the BS.At this time, when confirming a measurement duration allocated to apreferred-wide beam using the beam pattern information, the terminal candetect narrow beam reference signals only during the measurementduration and measure a reception signal strength for the narrow beamreference signals. Also, when confirming a measurement durationallocated to a preferred-wide beam according to a predefinedcorresponding relationship therebetween, the terminal can detect narrowbeam reference signals only during the measurement duration and measurethe reception signal strength for the narrow beam reference signals.Also, when confirming only the number of narrow beam reference signalsthrough the beam pattern information, the terminal can detect all thenarrow beam reference signals during a measurement durationcorresponding to the number of narrow beam reference signals and measurea reception signal strength for the narrow beam reference signals.

After measuring the reception signal strength for the narrow beamreference signals, the terminal proceeds to step 809 and transmits afeedback signal notifying the preferred-narrow beam to the BS. Thefeedback signal includes information indicating the preferred-narrowbeam of the terminal The information indicating the preferred-narrowbeam of the terminal can include an index of a reference signal or anindex of a beam.

The method described above in relation with FIG. 9 under of the presentinvention may be provided as one or more instructions in one or moresoftware modules, or computer programs stored in an electronic deviceincluding the terminal.

FIG. 9 illustrates a construction of a BS in a wireless communicationsystem according to an exemplary embodiment of the present invention.

Referring to FIG. 9, the BS includes a controller 910, a modem 920, atransmission Radio Frequency (RF) chain 930, a beamforming unit 940, anantenna array 950, and a receiver 960.

The modem 920 performs a function of conversion between a basebandsignal and a bit stream according to the physical layer standard of thesystem. For example, according to an OFDM scheme, at data transmission,the modem 920 creates complex symbols by encoding and modulating atransmission bit stream, maps the complex symbols to subcarriers, andthen constructs OFDM symbols through Inverse Fast Fourier Transform(IFFT) operation and Cyclic Prefix (CP) insertion. Also, at datareception, the modem 920 divides a baseband signal in the unit of OFDMsymbol, restores signals mapped to subcarriers through Fast FourierTransform (FFT) operation, and restores a reception bit stream throughdemodulation and decoding. The receiver 960 converts an RF signalreceived from a terminal into a baseband digital signal. Although notillustrated in detail, the receiver 960 includes an antenna, a receptionRF chain and the like.

The transmission RF chain 930 converts a baseband digital signal streamprovided from the modem 920 into an RF band analog signal. For instance,the transmission RF chain 930 can include an amplifier, a mixer, anoscillator, a Digital to Analog Converter (DAC), a filter, and the like.The BS can simultaneously form as many transmission beams as the numberof the transmission RF chains 930.

The beamforming unit 940 performs transmit beamforming for atransmission signal provided from the transmission RF chain 930. Forexample, the beamforming unit 940 includes a plurality of phaseconverters, a plurality of amplifiers, and a signal summing unit. Thatis, the beamforming unit 940 divides a transmission signal provided fromeach of the transmission RF chains 930 as many as a plurality ofantennas included in the antenna array 950, and adjusts a phase of eachof the divided signals. Also, the beamforming unit 940 sums up signalsto be transmitted by the same antenna. The antenna array 950 is a set ofthe plurality of antennas, and includes a plurality of array elementsand radiates signals provided from the beamforming unit 940 over awireless channel.

The controller 910 controls a general operation of the BS. For example,the controller 910 generates and provides a transmission traffic packetand a message to the modem 920, and interprets a reception trafficpacket and a message provided from the modem 920. Particularly, thecontroller 910 controls to perform a beam acquisition procedure. Anoperation of the controller 910 for the beam acquisition procedure isdescribed as follows.

The controller 910 determines if terminals are uniformly distributedwithin the service coverage of the BS. When the terminals are uniformlydistributed within the service coverage of the BS, the controller 910controls the modem 920 and the beamforming unit 940 to repeatedlytransmit narrow beam reference signals in all directions within theservice coverage. In contrast, when the terminals are randomlydistributed within the service coverage of the BS, the controller 910controls the modem 920 and the beamforming unit 940 to repeatedlytransmit wide beam reference signals in all directions within theservice coverage. And, the controller 910 determines a direction rangethat is to transmit narrow beam reference signals depending onpreferred-wide beams of terminals and then, controls the modem 920 andthe beamforming unit 940 to transmit the narrow beam reference signalswithin the determined range. And, the controller 910 confirmspreferred-wide beams that the terminals prefer and preferred-narrowbeams that the terminals prefer, through a feedback signal receivedthrough the receiver 960.

When transmitting the narrow beam reference signals, the controller 910determines transmission patterns of the narrow beam reference signals.For example, as illustrated in FIG. 4 and FIG. 5, when measurementdurations during which narrow beam reference signals are transmitted arecontinuous irrespective of the results of selection of preferred-widebeams, the controller 910 determines the number of measurement durationsthat are to transmit the narrow beam reference signals, depending on thenumber of preferred-wide beams of at least one terminal And, thecontroller 910 allocates the continuous measurement durations to thepreferred-wide beams, and determines to transmit narrow beam referencesignals through a measurement duration allocated to a correspondingpreferred-wide beam. For another example, as illustrated in FIG. 6, whenthe distribution of measurement durations during which narrow beamreference signals are transmitted becomes different depending on theresults of selection of preferred-wide beams, the controller 910confirms a position of at least one measurement duration correspondingto a preferred-wide beam of at least one terminal according to apredefined corresponding relationship therebetween, and determines totransmit narrow beam reference signals through a measurement durationcorresponding to a corresponding preferred-wide beam. After determiningthe transmission patterns of the narrow beam reference signals, thecontroller 910 transmits beam pattern information notifying thetransmission patterns of the narrow beam reference signals. However,when a corresponding relationship between a preferred-wide beam and ameasurement duration is predefined, transmission of the beam patterninformation can be omitted.

FIG. 10 illustrates a construction of a terminal in a wirelesscommunication system according to an exemplary embodiment of the presentinvention.

As illustrated in FIG. 10, the terminal includes an antenna array 1010,a beamforming unit 1020, a reception RF chain 1030, a modem 1040, atransmitter 1050, and a controller 1060.

The antenna array 1010 is a set of a plurality of antennas, and includesa plurality of array elements. The beamforming unit 1020 performsreceive beamforming for signals received through the plurality ofantennas constructing the antenna array 1010. For example, thebeamforming unit 1020 includes a plurality of amplifiers, a plurality ofphase converters, and a signal summing unit. For example, thebeamforming unit 1020 adjusts and sums up phases of the signals receivedthrough the plurality of antennas, thereby performing the receivebeamforming. The reception RF chain 1030 converts an RF-band analogreception signal into a baseband digital signal. For example, thereception RF chain 1030 can include an amplifier, a mixer, anoscillator, an Analog to Digital Converter (ADC), a filter, and thelike.

The modem 1040 performs a function of conversion between a basebandsignal and a bit stream according to the physical layer standard of thesystem. For example, according to an OFDM scheme, at data transmission,the modem 1040 creates complex symbols by encoding and modulating atransmission bit stream, maps the complex symbols to subcarriers, andthen constructs OFDM symbols through IFFT operation and CP insertion.Also, at data reception, the modem 1040 divides a baseband signalprovided from the reception RF chain 1030 in the unit of OFDM symbol,restores signals mapped to subcarriers through FFT operation, andrestores a reception bit stream through demodulation and decoding.

Particularly, the modem 1040 measures a reception signal strength forreference signals received from a BS. In detail, the modem 1040 detectswide beam reference signals and narrow beam reference signals receivedfrom the BS, measures a reception signal strength for each of thereference signals, and then provides the measured reception signalstrengths of the reference signals to the controller 1060. At this time,the modem 1040 detects the narrow beam reference signals according tocontrol of the controller 1060. For example, when confirming ameasurement duration allocated to a preferred-wide beam using beampattern information provided from the BS, the modem 1040 can detectnarrow beam reference signals only during the measurement duration, andmeasure reception signal strengths of narrow beam reference signals.Also, when confirming a measurement duration allocated to apreferred-wide beam according to a predefined corresponding relationshiptherebetween, the modem 1040 can detect narrow beam reference signalsonly during the measurement duration, and measure reception signalstrengths of the narrow beam reference signals. Also, when confirmingonly the number of narrow beam reference signals through the beampattern information, the modem 1040 can detect all the narrow beamreference signals during a measurement duration corresponding to thenumber of narrow beam reference signals, and measure reception signalstrengths of the narrow beam reference signals.

The transmitter 1050 converts a transmission signal provided from themodem 1040 into an RF band signal and transmits the RF band signal tothe BS. Although not illustrated in detail, the transmitter 1050includes a transmission RF chain, an antenna and the like.

The controller 1060 controls a general function of the terminal. Forinstance, the controller 1060 generates and provides a transmissiontraffic packet and a message to the modem 1040, and interprets areception traffic packet and a message provided from the modem 1040.Particularly, the controller 1060 controls to perform a beam acquisitionprocedure. An operation of the controller 1060 for the beam acquisitionprocedure is described as follows.

The controller 1060 determines a preferred-wide beam and apreferred-narrow beam using reception signal strengths of wide beamreference signals and narrow beam reference signals received from theBS. And, the controller 1060 transmits a feedback signal notifying thepreferred-wide beam and a feedback signal notifying the preferred-narrowbeam, to the BS through the transmitter 1050. Particularly, thecontroller 1060 confirms transmission patterns of narrow beam referencesignals, for the sake of detection of the narrow beam reference signals.According to an exemplary embodiment of the present invention, thecontroller 1060 can determine transmission patterns of narrow beamreference signals depending on beam pattern information provided fromthe BS. In detail, the controller 1060 receives the beam patterninformation notifying the transmission patterns of the narrow beamreference signals from the BS and, through the beam pattern information,determines the number of narrow beam reference signals to betransmitted. And, the controller 1060 confirms a measurement durationallocated to the preferred-wide beam through the beam patterninformation. Here, the measurement duration allocated to thepreferred-wide beam is determined according to the order of an index ofa preferred-wide beam that the terminal prefers among the wholepreferred-wide beams. According to another exemplary embodiment of thepresent invention, the controller 1060 confirms a measurement durationcorresponding to a preferred-wide beam according to a predefinedcorresponding relationship therebetween. In detail, the controller 1060is aware of a predefined corresponding relationship between apreferred-wide beam and a measurement duration irrespective of thenumber and direction of preferred-wide beams and, according to this, thecontroller 1060 can confirm a corresponding measurement durationaccording to the order of an index of a preferred-wide beam that theterminal prefers among the whole preferred-wide beams.

It will be appreciated that embodiments of the present inventionaccording to the claims and description in the specification can berealized in the form of hardware, software or a combination of hardwareand software.

Any such software may be stored in a computer readable storage medium.The computer readable storage medium stores one or more programs(software modules), the one or more programs comprising instructions,which when executed by one or more processors in an electronic device,cause the electronic device to perform a method of the presentinvention.

Any such software may be stored in the form of volatile or non-volatilestorage such as, for example, a storage device like a ROM, whethererasable or rewritable or not, or in the form of memory such as, forexample, RAM, memory chips, device or integrated circuits or on anoptically or magnetically readable medium such as, for example, a CD,DVD, magnetic disk or magnetic tape or the like. It will be appreciatedthat the storage devices and storage media are embodiments ofmachine-readable storage that are suitable for storing a program orprograms comprising instructions that, when executed, implementembodiments of the present invention.

Accordingly, embodiments provide a program comprising code forimplementing apparatus or a method as claimed in any one of the claimsof this specification and a machine-readable storage storing such aprogram. Still further, such programs may be conveyed electronically viaany medium such as a communication signal carried over a wired orwireless connection and embodiments suitably encompass the same.

The present invention may be implemented in an electronic deviceincluding a portable terminal such as, for example, a smart phone and amobile telecommunication terminal. Hereunder, a portable terminal isused as an example for the electronic device.

As described above, exemplary embodiments of the present inventiondetermine transmission ranges of reference signals beamformed withnarrow beams for high gain using a wide beam inducing a relatively lessoverhead, thereby being able to determine the best beam by a minimumoverhead.

While the invention has been shown and described with reference tocertain preferred embodiments thereof, it will be understood by thoseskilled in the art that various turns in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for operating a base station (BS) in awireless communication system, the method comprising: transmittingprimary reference signals having a first beam width; receiving a firstfeedback signal indicating at least one primary preferred-beam havingthe first beam width from at least one terminal; transmitting secondaryreference signals having beam directions within a range determined basedon the at least one primary preferred-beam and having a second beamwidth; and receiving a second feedback signal indicating at least onesecondary preferred-beam having the second beam width from the at leastone terminal, wherein the first beam width is greater than the secondbeam width.
 2. The method of claim 1, wherein the range comprises apropagation range of the at least one primary preferred-beam.
 3. Themethod of claim 1, wherein the transmitting of the secondary referencesignals comprises: determining a total number of measurement durationscarrying the secondary reference signals based on a total number of theat least one primary preferred-beam; and transmitting the secondaryreference signals through the measurement durations.
 4. The method ofclaim 1, further comprising: transmitting information on allocation ofat least one measurement duration carrying the secondary referencesignals to the at least one terminal.
 5. The method of claim 4, whereinthe information comprises at least one of: at least one index of the atleast one primary preferred-beam, at least one combination of at leastone index of the at least one primary preferred-beam and at least oneindex of a corresponding at least one measurement duration, a totalnumber of the secondary reference signals, a total number of measurementdurations carrying the secondary reference signals, a total number ofthe at least one primary preferred-beams, and an index of the last oneof the measurement durations.
 6. The method of claim 1, wherein thetransmitting of the secondary reference signals comprises: identifyingat least one measurement duration corresponding to the at least oneprimary preferred-beam based on a predefined corresponding relationshipthere between; and transmitting the secondary reference signals throughthe at least one measurement duration.
 7. The method of claim 6, whereinthe transmitting of the secondary reference signals comprisestransmitting a subset of the secondary reference signals, having beamdirections within a propagation range of an n^(th) primary referencesignal , through a n^(th) measurement duration.
 8. The method of claim1, further comprising: if a distribution of terminals is substantiallyuniform within a service coverage of the BS, transmitting the secondaryreference signals in all directions of the service coverage, withouttransmission of the primary reference signals.
 9. The method of claim 1,wherein the at least one primary preferred-beam comprises a firstprimary preferred-beam and a second primary preferred-beam, wherein thetransmitting of the secondary reference signals comprises: transmittinga first subset of the secondary reference signals through a firstmeasurement duration corresponding to the first primary preferred-beam;and transmitting a second subset of the secondary reference signalsthrough a second measurement duration corresponding to the secondprimary preferred-beam, wherein beam directions of the first subset ofthe secondary reference signals are within a propagation range of thefirst primary preferred-beam, and wherein beam directions of the secondsubset of the secondary reference signals are within a propagation rangeof the second primary preferred-beam.
 10. A method for operating aterminal in a wireless communication system, the method comprising:receiving at least one of primary reference signals having a first beamwidth, from a base station (BS); transmitting a first feedback signalindicating a primary preferred-beam having the first beam width, to theBS; receiving at least one of secondary reference signals having beamdirections within a range determined based on the primary preferred-beamand having a second beam width; and transmitting a second feedbacksignal indicating a secondary preferred-beam having the second beamwidth, to the BS, wherein the first beam width is greater than thesecond beam width.
 11. The method of claim 10, further comprising:receiving information on allocation of at least one measurement durationcarrying the secondary reference signals from the BS.
 12. The method ofclaim 11, wherein the information comprises at least one of: at leastone index of the at least one primary preferred-beam, at least onecombination of at least one index of at least one primary preferred-beamand at least one index of a corresponding at least one measurementduration, a total number of the secondary reference signals, a totalnumber of measurement durations carrying the secondary referencesignals, a total number of the at least one primary preferred-beams, andan index of the last one of the measurement durations.
 13. The method ofclaim 10, wherein the receiving of the at least one of the secondaryreference signals comprises; identifying a measurement durationcorresponding to the primary preferred-beam; and detecting the at leastone of the secondary reference signals during the measurement duration.14. The method of claim 13, wherein the measurement durationcorresponding to the primary preferred-beam is identified based on anorder of an index of the primary preferred-beam.
 15. The method of claim10, wherein the receiving of the at least one of the secondary referencesignals comprises, identifying a total number of the second referencesignals; and detecting as many secondary reference signals as the totalnumber of the secondary reference signals during at least onemeasurement duration.
 16. The method of claim 10, wherein the receivingof the at least one of the secondary reference signals comprises:determining a measurement duration corresponding to the primarypreferred-beam based on a predefined corresponding relationship therebetween; and detecting the at least one of the secondary referencesignals during the measurement duration.
 17. The method of claim 10,wherein the receiving of the at least one of the secondary referencesignals comprises receiving a subset of the secondary reference signalsthrough a measurement duration corresponding to the primarypreferred-beam, wherein beam directions of the subset of the secondaryreference signals are within a propagation range of the primarypreferred-beam.
 18. An apparatus for a base station (BS) in a wirelesscommunication system, the apparatus comprising: a beamforming unitconfigured to beamform reference signals with a first beam width and asecond beam width; a transceiver configured to transmit the referencesignals to at least one terminal and to receive at least one feedbacksignal indicating at least one preferred-beam from the at least oneterminal; and a controller configured to control to transmit primaryreference signals having a first beam width, receive a feedback signalindicating at least one primary preferred-beam having the first beamwidth from at least one terminal, transmit secondary reference signalshaving beam directions within a range determined based on the at leastone primary preferred-beam and having a second beam width, and, receivea second feedback signal indicating at least one secondarypreferred-beam having the second beam width from the at least oneterminal, wherein the first beam width is greater than the second beamwidth.
 19. The apparatus of claim 18, wherein the range comprises apropagation range of the at least one primary preferred-beam.
 20. Theapparatus of claim 19, wherein the controller determines a total numberof measurement durations carrying the secondary reference signals basedon a total number of the at least one primary preferred-beam, andwherein the transceiver transmits the secondary reference signalsthrough the measurement durations.
 21. The apparatus of claim 19,wherein the transceiver transmits information on allocation of at leastone measurement duration carrying the secondary reference signals, tothe at least one terminal.
 22. The apparatus of claim 21, wherein theinformation comprises at least one of: at least one index of the atleast one primary preferred-beam, at least one combination of at leastone index of the at least one primary preferred-beam and at least oneindex of a corresponding at least one measurement duration, a totalnumber of the secondary reference signals, a total number of measurementdurations carrying the secondary reference signals, a total number ofthe at least one primary preferred-beams, and an index of the last oneof the measurement durations.
 23. The apparatus of claim 19, wherein thecontroller identifies at least one measurement duration corresponding tothe at least one primary preferred-beam based on a predefinedcorresponding relationship there between, and wherein the transceivertransmits the secondary reference signals through the at least onemeasurement duration.
 24. The apparatus of claim 23, wherein thetransceiver transmits a subset of the secondary reference signals,having beam directions within in a propagation range of an n^(th)primary reference signal, through a n^(th) measurement duration.
 25. Theapparatus of claim 18, wherein, if a distribution of terminals issubstantially uniform within a service coverage of the BS, wherein thetransceiver transmits the secondary reference signals in all directionsof the service coverage, without transmission of the primary referencesignals.
 26. The apparatus of claim 18, wherein the at least one primarypreferred-beam comprises a first primary preferred-beam and a secondprimary preferred-beam, wherein the transceiver transmits a first subsetof the secondary reference signals through a first measurement durationcorresponding to the first primary preferred-beam, and, transmits asecond subset of the secondary reference signals through a secondmeasurement duration corresponding to the second primary preferred-beam,wherein beam directions of the first subset of the secondary referencesignals is within a propagation range of the first primarypreferred-beam, and wherein beam directions of the second subset of thesecondary reference signals is within a propagation range of the secondprimary preferred-beam.
 27. An apparatus for a terminal in a wirelesscommunication system, the apparatus comprising: a transceiver configuredto receive reference signals from a base station (BS) and to transmitfeedback signals to the BS; a controller configured to control toreceive at least one of primary reference signals having a first beamwidth from the BS, to transmit a first feedback signal indicating aprimary preferred-beam having the first beam width, to the BS, toreceive at least one of secondary reference signals having beamdirections within a range determined based on the primary preferred-beamand having a second beam width, and, to transmit a second feedbacksignal indicating a secondary preferred-beam having the second beamwidth, to the BS, wherein the first beam width is greater than thesecond beam width.
 28. The apparatus of claim 27, wherein thetransceiver receives information on allocation of at least onemeasurement duration carrying the secondary reference signals, from theBS.
 29. The apparatus of claim 28, wherein the information comprises atleast one of: at least one index of the at least one primarypreferred-beam, at least one combination of at least one index of atleast one primary preferred-beam and at least one index of acorresponding at least one measurement duration, a total number of thesecondary reference signals, a total number of measurement durationscarrying the secondary reference signals, a total number of the at leastone primary preferred-beams, and an index of the last one of themeasurement durations.
 30. The apparatus of claim 27, wherein thecontroller controls to identify a measurement duration corresponding tothe primary preferred-beam, and, wherein the transceiver detects atleast one of the secondary reference signals during the measurementduration.
 31. The apparatus of claim 30, wherein the measurementduration corresponding to the primary preferred-beam is identified basedon an order of an index of the primary preferred-beam.
 32. The apparatusof claim 27, wherein the controller identifies a total number of thesecondary reference signals, and wherein the transceiver detects as manysecondary reference signals beamformed during at one measurementduration.
 33. The apparatus of claim 27, wherein the controllerdetermines a measurement duration corresponding to the primarypreferred-beam based on a predefined corresponding relationship therebetween, and wherein the transceiver detects the at least one of thesecondary reference signals during the measurement duration.
 34. Theapparatus of claim 27, wherein the transceiver receives a subset of thesecondary reference signals through a measurement duration correspondingto the primary preferred-beam, wherein beam directions of the subset ofthe secondary reference signals is within a propagation range of theprimary preferred-beam.